The present invention relates to a transformer used in electrical equipment such as a microwave oven, a television receiver or the like and provided with an insulating material having a thermal conductivity higher than 10.sup.-3 cal/cm.sec..degree. C which insulating material is interposed between a coil and a core.
There have been devised and demonstrated various types of transformers. In the shell-type transformers in which a coil or winding consisting of conductors wound around a bobbin and insulated with special insulating covering paper is placed on the central leg of the core consisting of E- and I-type or only E-type laminates stacked, insulating paper sheets are placed between the core and the upper and lower ends of the coil. The bobbin is mainly made of polyamide or a phenolic resin, and the covering and insulating paper, polyethylene terephthalate or aramid. However, they have, in general, a considerably low thermal conductivity. In addition, even when insulating members are placed between the core and the coil, there still remain air gaps therebetween, because it is almost impossible to attain very intimate contact between the core and the coil.
Since there exist insulating members and air with a lower thermal conductivity between the core and the coil, thermal resistance is quite high in the prior art transformers. As a result, the quick transfer of heat generated in the coil to the core cannot be attained, resulting in a considerable temperature rise of the coil. One method for overcoming this problem is to use conductors with a relatively large diameter and hence with a relatively low resistance so that the generation of Joule heat may be minimized. However, when conductors with a greater diameter are selected, the coil becomes large in size so that the core must also be made large in size. Therefore the consumption of copper and iron is increased with the resultant increase in manufacturing cost. This is a waste of precious natural resources, and it is the social responsibility placed on every manufacturer to make full use of scarce and precious natural resources.